1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to a system and method for the early detection of cellular piracy, more particularly to a system and method where the system operator can take action to stop unauthorized system use upon activation of a piracy alarm signal.
2. Description of the Related Art
The evolution of wireless communication over the past century, since Guglielmo Marconi's 1897 demonstration of radio's ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi's discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue to rise in the coming decades as well, as this wireless network interacts with and eventually overtakes the existing wireline networks.
In order to promote compatibility of the equipment and operations of various Public Land Mobile Networks (PLMN), air-interface standards have been developed and are currently being implemented. In North America, the most widely used standard protocol is the Advanced Mobile Phone System (AMPS), which is now being supplemented by a digital version (D-AMPS). Another such standard is the Global System for Mobile Communications (GSM), used throughout Europe and in some parts of the United States. In each standard, PLMN operators set up permanent equipment to cover a given geographical area and enlist mobile subscribers. The subscriber is billed by the operator for cellular service, generally paying a base charge in addition to a variable charge based on the subscriber's use of the system.
Unfortunately, along with the popularity of cellular telephone has come cellular piracy. A pirate scans the air interface for cellular phones initiating a connection with the PLMN, exploiting initialization procedures. To begin a call, a cellular Mobile Station (MS) first transmits a signal over the air interface that includes unique MS identifying information. This identification information indicates that access to the cellular system is being requested by a system subscriber, and is used by the PLMN for, among other things, billing the subscriber for the call. An eavesdropping pirate who intercepts this initial transmission can then replicate the signal and construct a "clone," that is, an MS that transmits identical identification information.
When the clone thereafter initiates a call using the subscriber's identity, the PLMN cannot distinguish between the pirate caller and the legitimate subscriber; system access will be granted to both. The geographical location of the clone is no help in making any distinction, since the subscriber can "roam," that is, make and receive calls while located outside its home service area. Of course, the legitimate subscriber is billed for all the usage. Pirates often operate a single clone for approximately one month, after which time the subscriber will likely receive and protest an inordinately high cellular service bill. Although steps can then be taken to avoid further unauthorized use, the PLMN operator generally bears the cost of the calls already made by the clone, resulting in the loss of thousands of dollars of air-time revenue. This problem is most acute in PLMNs operating under the AMPS/D-AMPS protocols, which lack the techniques available, for example, as in the GSM environment.
At present, enforcement against pirates is difficult at best. Clones are quickly abandoned after short periods of high use, after which the pirate acquires another cloned identity. Accordingly, there exists a need for a way to detect clone use earlier so that unauthorized use may be stopped and an attempt made to track down the pirate before large amounts of air time are stolen.